The disclosure of Japanese Patent Application No. 2000-261243 filed on Aug. 30, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The present invention relates to a drive force control system for an automotive vehicle, and more particularly to a control system and method for controlling a drive force of an automotive vehicle having a front drive device for driving front wheels and a rear drive device for driving rear wheels.
2. Description of Related Art
JP-A-7-117512 discloses an example of a drive force control system for an automotive vehicle having a front drive device arranged to drive the front wheels of the vehicle, and a rear drive device arranged to drive the rear wheels. The drive force control system disclosed in this publication is adapted such that the rear-wheel drive torque to be produced by the rear drive device is increased by an amount corresponding to an amount of reduction of the front-wheel drive torque produced by the front drive device when the front-wheel drive torque is reduced in a traction control for the front drive wheels.
The vehicle drive force control system of the type described above prevents deterioration of the drivability and/or acceleration performance of the vehicle by increasing the rear-wheel drive torque by the amount corresponding to the amount of reduction of the front-wheel drive torque produced by the front drive device. This vehicle drive force control system is further arranged such that the rear-wheel drive torque produced by the rear drive device does not exceed the front-wheel drive torque produced by the front drive device. This arrangement is effective in preventing an oversteering behavior of the vehicle, and improves the straight-line acceleration stability of the vehicle.
In the known vehicle drive force control system described above, however, the front-wheel and rear-wheel drive forces are basically controlled so as to optimize the proportion of the front and rear-wheel drive forces depending upon the running condition of the vehicle, in substantially the same manner as in the conventional drive force control system for four-wheel-drive (4WD) vehicles. Namely, this vehicle drive force control system is not designed with enough considerations to assure optimum control of the front and rear-wheel drive forces during turning of the vehicle. Accordingly, further improvements are needed in this vehicle drive force control system to further optimize the control of the vehicle drive force during an unstable state of turning of the vehicle with a relatively large amount of lateral slipping of the wheels, or during traction control of the front wheels during turning of the vehicle.
It is therefore an object of this invention to improve the turning stability and drivability of the vehicle by further optimizing the control of the front-wheel and rear-wheel drive forces to be produced by the respective front and rear-wheel drive devices during turning of the vehicle.
This object may be achieved according to a first aspect of this invention, which provides a drive force control system for an automotive vehicle, having a front-wheel drive device for driving front wheels of the vehicle, a rear-wheel drive device for driving rear wheels of the vehicle, where one of the front-wheel and rear-wheel drive devices serving as a primary drive device of the vehicle while the other of the front-wheel and rear-wheel drive devices serving as an auxiliary drive device of the vehicle, and a drive-force controller operable when an amount of lateral slip of the wheels is larger than a predetermined threshold to reduce a drive force to be produced by the primary drive device, and to reduce a drive force to be produced by said auxiliary drive device by an amount irrespective of an amount of reduction of the drive force of said primary drive device.
In the vehicle drive force control system described above, the drive force of the auxiliary drive device may be reduced to zero.
This object may also be achieved according to a second aspect of this invention, which provides a drive force control system for an automotive vehicle, having a front-wheel drive device for driving front wheels of the vehicle, a rear-wheel drive device for driving rear wheels of the vehicle and a drive-force controller operable to reduce a drive force to be produced by the front-wheel drive device depending upon a slipping state of the front wheels being drive by the front-wheel drive device, and to reduce a drive force to be produced by the rear-wheel drive device depending upon an angle of turning of the vehicle.
In the vehicle drive force control system constructed according to the first aspect of this invention, the drive-force controller is operated when the vehicle is turning during low stability with a relatively large amount of lateral slip of the wheels. This operation allows the drive force produced by the primary drive device to be reduced while the drive force produced by the auxiliary drive device is reduced by an amount irrespective of the amount of reduction of the drive force of the primary drive device. Thus, the amount of reduction of the drive force of the auxiliary drive device can be controlled freely from the amount of reduction of the drive force of the primary drive device. Accordingly, this operation allows the present vehicle drive force control system to enable the vehicle operator to manipulate the braking system of the vehicle. The vehicle drive force control system can also adjust the vehicle running stability control apparatus of braking force control type to effectively decelerate the turning vehicle. Accordingly, the vehicle drive force control system is more effectively able to increase the vehicle turning stability than the known vehicle drive force control system.
In the vehicle drive force control system according to the second aspect of this invention, the drive-force controller is operated to reduce the drive force of the front-wheel drive device, depending upon the slipping state of the front wheels being driven by the front-wheel drive device, and to reduce a drive force of the rear-wheel drive device, depending upon the angle of turning of the vehicle. When the vehicle is turning while the front wheels being driven by the front-wheel drive device are slipping, the drive force of the rear wheels is reduced with an increase in the turning angle of the vehicle. This situation can sometimes increase the likelihood of deterioration of the turning stability of the vehicle. However, the vehicle drive force control system according to the second aspect of this invention prevents the deterioration of the turning stability of the vehicle due to an excessively large drive force of the rear wheels.
This object may also be achieved according to a third aspect of this invention, which provides a method of controlling a drive force of an automotive vehicle including a front-wheel drive device for driving front wheels of the vehicle, and a rear-wheel drive device for driving rear wheels of the vehicle, where one of the front-wheel and rear-wheel drive devices serves as a primary drive device of the vehicle, while the other of the front-wheel and rear-wheel drive devices serves as an auxiliary drive device of the vehicle. This method comprises the steps of detecting an amount of lateral slip of the wheels, reducing a drive force to be produced by the primary drive device when the amount of lateral slip of the wheels is larger than a predetermined threshold, and reducing a drive force to be produced by the auxiliary drive device by an amount irrespective of an amount of reduction of the drive force of the primary drive device when the amount of lateral slip is larger than the predetermined threshold.
The object indicated above may also be achieved according to a fourth aspect of this invention, which provides a method of controlling a drive force of an automotive vehicle that includes a front-wheel drive device for driving front wheels of the vehicle, and a rear-wheel drive device for driving rear wheels of the vehicle. This method comprises the steps of reducing a drive force to be produced by the front-wheel drive device, depending upon a slipping state of the front wheels being driven by the front-wheel drive device, and reducing a drive force to be produced by the rear-wheel drive device, depending upon an angle of turning of the vehicle.